Pulse-blocking circuit



Sept. 11, 1951 H. J. LlPKlN 2,567,851

PULSE-BLOCKING CIRCUIT Filed Aug. 1, 1945 2 Sheets-Sheet 2 AAAAAA IVVVVIVV w64 ll INVENTOR HARRY J. LIPKIN ATTORNEY Patented Sept. 11,. 1951 PULSE-BLOCKING CIRCUT'I Harry J. Lipkin, Dorchester, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application August 1, 1945, Serial No: 608,315

Claims.

This invention relates in general to electrical circuits and more particularly to electrical pulsegenerating circuits.

For some purposes in radio pulse communication it is desired to generate a pulse of a given shape, the time of starting of this pulse being dependent upon the time of application of a triggerj pulse to the circuit. In certain types of radio object-detection apparatus, and in other instances, this trigger pulse emanates from a series of thermionic tube amplifier stages the overall bandwidth of which is narrow with respect to the bandwidth of an appreciable portion of the energy contained in the trigger pulse. One reason for using a relatively narrow overall bandwidth is the necessity in some instances for a high gain in the trigger pulse amplifier stages. Since relatively wide stage bandwidth may be sacrificed for a higher gain, the overall bandwidth is often relatively narrow in such circuits. The important effects resulting from such a relatively narrow overall. bandwidth are twofold. Firstly, the'output pulse from these stages is greatly distorted with respect to the input pulse.

Secondly, the transient response of these stages is such that a few cycles of damped oscillations may beadded onto the pulse, the amplitude of the first few of these waves often being of the same order of magnitude as that of the main pulse, These oscillations are undesirable in that they contain information other than that embodied in the main pulse. Accordingly, the circuits into which this trigger pulse feeds must be such that they are insensitive to the aforemen tioned oscillations.

Among therefore, are:

1. To provide electrical circuits for the generation of pulses;

2. To provide such circuits which may be synchronized by a trigger pulse; and

3. To provide such circuits which are substantially insensitive to oscillations which may occur in the wake of such a trigger pulse.

f In accordance with the present invention there are illustrated several embodiments of a triggered pulse-generating circuit. One embodiment provides a triggered multivibrator with one tube normally non-conducting. The substantially rectangular pulse output of the multivibrator is coupled to an amplifier tube biased beyond cutoff. This pulse does not appear at the output of the amplifier tube until the associated input capacitance of the tube is partially charged, and so a time delay is obtained.

the objects of the present invention,.

Another embodiment of the circuit provides a multivibrator with one tube caused to be non conducting by the impressing of a positive potential on its cathode. Unbypassed resistors are placed in the cathode circuits of both tubes, and the output is taken from one of these cathode resistors. 1

still another embodiment provides a multivibrator having a normally non-conducting tube. The output of the multivibrator is coupled through a diode to an amplifier tube. A pulse with oscillations following it may be fed to the multivibrator, in which case the output of the amplifier does not contain the -pscillations, and

' also preserves the original pulse length.

There is also described a multivibrator circuit with the grid of one of the tubes connected to a point of negative potential, so as to render this tube normally non-conductive. A negative trig-i ger pulse applied to the grid of the normallyconducting tube cuts this tube off and turns the former tube on. After a time dependent upon the constants of the. circuit the multivibrator. switches back to its quiescent condition. A substantially rectangular pulse is generated thereby,

the length of which is dependent upon the constants of the circuit.

This invention will best be understood by reference to the drawings, in which:' Fig. 1 is a circuit diagram of a triggered multi vibrator and amplifier having a time delay;

Fig. 2 is a circuit diagramof a triggered multivibrator; 4 v Fig. 3 is a circuit diagram of anarrangement' which substantially maintains the input pulse length; and I Fig. 4 is a circuitdiagram of a triggered mu1ti-. vibrator. v 1

Referring now to a description of the invention and to Fig. 1, the trigger pulse 35, which islabeled as such, is coupledto the grid ll) of the'nori. mally-conducting tube ll of the multivibrator. This grid is returned to a point of positive potential, B+, through grid-leak resistor [2. The plate I3 is connected to 13+ through plate load. resistor 14. The cathode [5 of tube His connected directly to the cathode'l 6 of the normally non-conducting tube I! of the multivibrator, and; both cathodes are tied to ground throughresistor H3. The grid I9 of tube I1 .is also connectedto' ground through grid-leak resistor 20. The plate 2| of tube 11 is connected to 3+ through plate' load resistor 22, and is coupled back to the grid of tube I I by condenser 23'. The plate of tube H a is coupled to the grid of tube I! by condenser 24:-

The output of the multivibrator, shown as pulse 33, is taken from the plate of tube H, and is coupled through condenser 25 to the grid 25 of amplifier tube 21. The grid of this tube is tied to a point of negative potential through grid-leak resistor 28. The plate 20 of tube 2". is connected to B+ through plate load resistor 30, and the cathode 3| is grounded. The input capacitance of tube 21 plus the pertinent wiring capacitance is represented by condenser 32. The output pulse, shown as pulse 34, is taken from the plate of tube 21. The time axis marked on pulses 35, 33 and 34 represents the time of occurrence of the leading edge of the trigger pulse 35.

Referring now to Fig. 2, a negative pulse as noted, is coupled to the grid of the normallyconducting tube 4| of the multivibrator. This grid is tied to ground through grid-leak resistor 42. The cathode 44 of tube 4| is connected to ground through cathode resistor 43. The plate 45 is connected to a point of positive potential, B+, through plate load resistor 49, and is coupled to the grid 41 of the normally non-conducting tube 48 of the multivibrator through condenser 49. This grid 4! is tied to ground through gridleak resistor 50. The cathode 5| of tube 48 is held at a positive potential by a voltage divider, connected between 13+ and ground, consisting of resistors 52 and 53 respectively. The plate 54 of this tube is connected to B+ through Plate load resistor 55, and is coupled back to the grid of tube 4| through condenser 58. The pulse output 58 of the circuit, as noted, is taken from the cathode 5|.

In the embodiment of Fig. 3 the input pulse 84, with trailing oscillations 82 and 83, is coupled to the grid 60' of the normally-conducting tube 6| of a multivibrator. This grid is tied to ground through grid-leak resistor 13 and the cathode 3.2 oftube 6| is grounded. The plate 63 is connected to a point of positive potential, B+, through plate load resistor 34, and is coupled to the grid 65 of the normally non-conducting tube 66 of the multivibrator through condenser 51. The grid 65 of tube 66 is tied to a point of negative potential through grid-leak resistor 69. The cathode 10 of this tube is grounded. The plate 68 of this tube is connected to B+ through plate load resistor 1|, and is coupled back to the grid of tube 6| through condenser 12.

The output of the multivibrator is taken from the plate of tube 6|, and is coupled through condenser 14 to grid-leak resistor 15, where it appears as pulse 85. The voltage across re sistor 15 is coupled through a diode 16 to the grid "of an amplifier tube 18. The cathode 82 of the diode T6 is connected to resistor 15, while the plate 83 is connected to the grid of tube 18, which is tied to ground through grid-leak resistor 86. The cathode 19 of amplifier tube 18 is grounded and the plate is connected to B+ through plate load resistor 8|. The output of the circuit, pulse 81, is taken from the plate of the amplifier tube.

Fig. 4 is a circuit diagram of another type of triggered multivibrator. A negative trigger pulse |04, with oscillations I05 and I08, is apapplied to the grid of the normally-conducting tube 9| of the multivibrator. This grid is tied to ground through grid-leak resistor 92. The cathode of tube 9| is grounded, and the plate 94 is connected to a point of positive potential, 13+, through plate load resistor 93. The plate 94 is also coupled through condenser 95 to the grid 91 of the normally non-conducting tube 98;

of the multivibrator. The grid of tube 98 is tied to a point of negative potential through grid-leak resistor 9-9, and the cathode |00 is grounded. The plate I03 of this tube 98 is connected to 3+ through plate load resistor WI, and is coupled back to the grid of tube 9| through condenser I02. The output pulse I01 is shown as being taken from the plate of tube 98.

The circuitof Fig. 1 is designed so that the output pulse will be formed at a small time delay with respect to the input pulse. Due to the positive grid return of tube II, this tube will be normally highly conducting. The current in this tube also flows through resistor l8, keeping the cathode of this tube, and the cathode of tube IT, at a positive potential. The cathode voltage of tube 11 may be sufficient to cut it off. Thus under normal conditions tube II will be highly conducting, while tube I! will be non-conducting.

A negative input pulse, or trigger 35, lowers the grid potential of tube and raises the plate potential thereof. This increase is coupled to the grid of tube H, which is also increased in voltage. This causes a decrease in voltage on the plate of tube H, which is coupled back to the grid of tube N. This cumulative action causes a rapid switching to occur in the multivibrator, with the result that tube becomes non-conducting, and tube 1 becomes conducting. This situation remains until the potential of the grid of tube H, which is steadily decreasing, reaches cutofi potential, at which time there is another rapid switching action which is the reverse of the first such action described, and the normal conditions are resumed with tube conducting and tube I1 non-conducting.

The output pulse of the multivibrator is taken from the plate of tube H and has a shape substantially like that shown at .33.. The waveiorm 33 does not build up to its maximum voltage instantaneously, but must first charge up the capacitance 32. It is noted that the leading edge of the pulse is sloping, the shape being exaggerated in waveform 33 for clarity. Since the grid of amplifier tube 21 is biased beyond cutoff, the potential of this grid must be raised a certain amount before this tube starts conduction. This grid potential cannot be raised instantaneously, but first the input capacitance of tube 21 must be charged to the correct potential. Thus there is a slight delay in the appearance of an output pulse 34 from the amplifier over the time the trigger pulse 35 first is applied to the input, this delay being due to the time it takes to charge this input capacitance to such a value that the grid reaches the cutoff potential. It is noted that the leading edge of wave 34 occurs a short time after the time marked 0, which is the time the leading edge of pulse 35 occurs.

One use for the abovementioned type of circuit is in a pulse communication system which is being operated in the near vicinity of a highpowered pulse transmitter. In this case it is necessary that the pulses from the nearby pulse transmitter be not able to be detected by the receiver containing this circuit. The is usually accomplished by turning 013 some of the receiver stages by means of a negative blanking pulse which is synchronized by the pulse from the pulse transmitter. This negative blanking pulse may be applied to the grids of these stages, and be of such an amplitude as to cut the associated tubes off. In order that the received pulse from the pulse transmitter not affect the receiver for even a small amount of time, the use of some such circuit as the abovementioned is necessary. The blanking pulse will then have enough time to turn off some of the receiver stages before the received pulse reaches these stages.

The circuit of Fig. 2 is another embodiment of a multivibrator-type pulse generator. A voltage divider from a point of positive potential B+, to ground, consisting of resistors 52 and 53 holds the cathode of tube 48 at a positivepotential, so that this tube is normally non-conducting. The other tube ll of the multivibrator is normallyconducting. A negative pulse 51, as shown, is applied to the grid of tube 4|, and by the conventional multivibrator action described in connection with Fig. 1, a condition quickly results in which tube 4| is non-conducting and tube 48 is conducting. This condition, which lastsforan amount of time which is dependent upon the circuit constants, exists until the voltage on the grid of tube 4-8, which is steadily decreasing, reaches cutoff, at which time the circuit quickly assumes the normal operating condition again. The output pulse 58 in this case is taken from the cathode of tube 43, which provides a low impedance output. It is understood, however, that the output may be taken from other points in the circuit.

One use of the circuit of Fig. 2 is in a pulse communication system which responds to groups of two pulses, the spacing of the pulses being of a certain given time duration. The circuit shown is incorporated in a receiver which is adapted to receive the first of the two pulses and to use it to trigger the multivibrator. The length of the generated pulse is made substantially equal to the aforementioned given time duration. This pulse may then be sent through an inverter stage and be used to turn on several stages of a second re ceiver which will be adapted to receive the second of the transmitted pulses. generated pulse is determined by the constants of the multivibrator circuit.

The circuit of Fig. 3 provides an output pulse which is substantiall of the same time duration as the input pulse. The circuit also is insensitive to any oscillations which mav occur after the original positive pulse. Tube fil is the normallyconducting and tube 66 is the normally nonconducting tube of a triggered multivibrator. Let us assume that the input pulse is of the shape shown, with the main portion 84 of the pulse being positive. Since it is applied to the normallyconducting tube, this pulse goes through the multivibrator without causing a switching action therein, and appears across resistor 15 as a negative pulse 85. Since this pulse is negative, conduction will occur in diode T6, and the pulse will be coupled to the grid of tube 18, and will appear on the plate of this tube as a positive pulse 81 of substantially the same length as the first positive portion 84 of the input pulse.

The negative portion 82 of the input pulse will start the conventional multivibrator switching action, with the condition then being one with tube 6| non-conducting and tube 66 conducting. Ac-- cordingly, a positive pulse is generated at the plate of tube at and will appear across resistor 15, but this will not be coupled to tube i8, since the diode 16 will not conduct with its cathode at such a high positive potential. The. second positive portion 83 of the input pulse is usually too small to be of consequence, since a relatively large positive pulse at the grid of tube 5! is needed at this point in the operation to cause the switching action to again occur.

The multivibrator circuit of Fig. 4 produces an The length of the output pulse It! the leading edge of which starts substantially at the time an input negative pulse N14 is applied. This circuit is insensitive to any oscillations which may occur after the trigger pulse I04. Tube 98 is normally non-conducting due to the negative bias placed on its grid, and tube 9! is normally-conducting. The negative input pulse 1 04 starts the conventional multivibrator switching action, so that substantially as soon. as this pulse is applied tube 9! becomes non conducting and tube 98 becomes conducting.

The incoming pulse may have oscillations I05 and I06 following it. As a result of the violent switching action of the circuit, however, the grid of tube 9| will be held at a potential far below cutolf, so positive pulse I05 of the oscillations will have no effect on the operation of the circuit. Negative pulse I06 will cause no switching action to occur because tube 9| is non-conducting. The time duration of the output pulse I07, shown negative for an example, will depend upon the constants of the circuit. While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. A. pulse-blockingcircuit comprising a quiescently-conducting first vacuum tube having'a cathode, anode, and at least one grid, the gridof said first vacuum tube being coupled to a point of positive potential; a second vacuum tube having a cathode, anode, and at least one grid, cathode-coupled to said first vacuum tube, whereby said second vacuum tub is quiescently cut off; a first capacitance means coupling the plate of said first vacuum tube to the grid of said second vacuum tube; a second capacitance means coupling the plate of said second vacuum tube to the grid of said first vacuum tube; means coupled to said first vacuum tube. for applying a first pulse from a source external to said circuit onto said circuit, whereby said first vacuum tube becomes cut off for a period of time and said second vacuum tube becomes conductive for substantially the same period of time, whereby apositive second pulse is formed at the plate 01' said first vacuum tube; a third vacuum tube having a cathode, anode, and at least one grid, coupled to the plate of said first vacuum tube, the grid of said third vacuum tube being connected to a point of negative potential, whereby said third vacuum tube is cut off in the absence of a first pulse; a third capacitance means connected between the input of said third vacuum tube and ground; whereby a third pulse is formed at the output of said third vacuum tube and the formation of said third pulse is delayed a period of time from the formation of said first pulse.

2. A pulse-blocking circuit comprising a quiescently-conducting first vacuum tube having a cathode, anode, and at least one grid; a second vacuum tube having a cathode, anode, and at least one grid; biasing means for applying a voltage to said second vacuum tube; whereby said second vacuum tube is quiescently cut off; first capacitance means coupling the plate of saidfirst vacuum tube to the grid of said second vacuum tube; second capacitance means coupling the plate of said second vacuum tube to the grid of said first vacuum tube ;v means applying a positive first pulse with oscillations thereafter from a point external to said circuit to the grid of said first vacuum tube; a third vacuum tube having a cathode, anode, and at least one grid; a diode vacuum tube coupling the plat of said first vacuum tube to the grid of said third vacuum tube; whereby said first pulse appears at the output of said third vacuum tube; whereby said oscillations after said first pulse cause said first vacuum tube to be cut off for a period of time and cause said second vacuum tube to conduct for substantially the same period of time, causing a positive second pulse to be started at the plate of said first vacuum tube substantially at the time said oscillations start, rendering said diode vacuum tube impervious .to current flow therethrough.

3. A pulse-blocking circuitincluding a one-shot multivibrator comprising a first vacuum tube, a second vacuum tube, said vacuum tubes being capacitively coupled to one another, said. first vacuum tube being adapted to respond to a, triggering pulse of electrical energy, which may be accompanied by undesired random pulses, and means for biasing said vacuum tubes so as to cause said first vacuum tube to be normally conducting and said second vacuum tube to be normally cut-01f; a third vacuum tube having a cathode, anode, and at least one control grid, said control grid being coupled through a coupling capacitor to the output of said first vacuum tube; whereby the action of said multivibrator serves to prevent any response of said third vacuum tube to said random pulses af-ter theoccurrence of said triggering pulse, during acycle of operation of said one-shot multivibrator.

4. A pulse-blocking circuit as set forthin claim 3 wherein said third Vacuum tube is normally cut-01f and has an integrating circuit including the grid. to cathode interelect'ro'de capacitance of said third vacuum tube, which serves to delay its response. to said triggering pulse for a given period of'time.

5'. A-pulse-blocking circuit as set forth in claim 3, and also including a diode vacuum tube having a cathode connected to said coupling capacitor and an-anode' connected to the grid of said'third vacuum tube, resistive means being connected fromthe grid of said third vacuum tube to ground, said third vacuum tube being normally conductive, whereby only the positive initial input pulse coupled to said first vacuum tube will be amplified by said third vacuum tube, the subsequent action of said multivibrator and said diode serving to prevent response of said third vacuum tube to later input signals.

HARRY J. LIPKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Time Bases by O, S. Puckle, Journal of the Institution of Electrical Engineers. Part III, Communication Engineering, June 1942, page 110. 

